Among the issues most commonly discussed are individuality, the rights of the individual, the limits of legitimate government, morality, history, economics, government policy, science, business, education, health care, energy, and man-made global warming evaluations. My posts are aimed at thinking, intelligent individuals, whose comments are very welcome.

26 November 2014

A Perspective on the "Greenhouse Effect" that Includes an Important Cooling Effect

Tony Heller at Real Science says that:

“The sun warms the Earth’s surface, which causes the Earth’s surface to emit longwave radiation.
Greenhouse gases like H2O and CO2 absorb certain wavelengths of longwave radiation emitted from the Earth’s surface. This adds energy to those molecules, which gets transferred to nearby molecules as heat. Without the greenhouse gas molecules, that energy would have been directly transmitted back into space without warming the atmosphere.”

Tony is right in this quote.  But the scale of such effects needs to be put into perspective relative to another effect of the infra-red active gases.  The solar insolation at the top of the atmosphere was 1365.8 W/m2 in 2010.  So on a cloudless day and with no infra-red active (so-called greenhouse) gases or gases that absorb ultra-violet light, there is a time when this 1365.8 W/m2 would be incident upon the Earth’s surface.  Let us examine the top of the atmosphere solar radiation spectrum and compare it with the solar radiation spectrum at the surface.

The atmospheric absorption in the UV and the visible range here is about 0.175 times the top of the atmosphere solar insolation, while that due to the absorption in the infra-red range is about 0.146 times the top of the atmosphere solar radiation.  If we assume an 8.8% reflection of solar radiation incident upon the surface, as was the case in the Kiehl-Trenberth Earth Energy Budget of 1997, then the solar radiation incident and not reflected from the surface is 845.77 W/m2.  The corresponding surface temperature assuming an emissivity of 0.95 would be 354.0K or 177.5ºF.  Of course, water evaporation and transport and air conduction and convection are powerful cooling effects so that conditions are rare when surfaces actually reach this temperature.

Now let us add back in the solar radiation absorbed by the infra-red active gases and make the same calculation.  The incident and not reflected solar power density would be 1027.63 W/m2.  The corresponding surface temperature would be 371.65K or 209.3ºF.  Without infra-red absorbing gases in the atmosphere, the mid-day temperature would rise by 17.65K or 31.8ºF, before the water evaporation and air conduction cooling effects lowered the surface temperature!

This cooling effect of infra-red active gases which only operates during the daylight hours has to be subtracted from such slowing of cooling effects due to the infra-red radiation emitted by the surface by those same infra-red active gases.  Now, I have only calculated a maximum mid-day effect and the cooling effect is smaller at other times and vanishes at night.  Meanwhile, the slowdown in the long wave surface emissions is an all-day effect.  Taken together, the two effects provide us with an important moderation of the temperature through the daily cycle.  The day to night temperature variations are reduced, very much to our advantage.

I believe the net warming (the slowdown in cooling effect) due to infra-red gases is smaller than the cooling effect in the daylight hours.  In other words, the net effect is a cooling effect.  This many will dispute with me, but there is a dawning awareness by many scientists that the net warming effect of infra-red gases is nowhere near the 33K warming commonly claimed by the proponents of the catastrophic man-made global warming hypothesis.  For those who believe that effect is much smaller, then it becomes very important to calculate the daytime cooling effect I have discussed here in comparison to the moderation of surface radiative cooling.  It is a travesty that these offsetting effects are not given proper attention in discussions of the effects of infra-red gases.

Of course water has a host of other heating and cooling effects at the surface and in the troposphere which also need to be carefully considered to determine its net role in our climate.  Also, while the absorption of surface-emitted longwave radiation warms the atmosphere, that warm atmosphere is more effective in transporting that warmth upward than back to the surface.

1 comment:

geran said...

Many good points in this posting, such as “It is a travesty that these offsetting effects are not given proper attention in discussions of the effects of infra-red gases.”

The posting begins by mentioning “Goddard”. He still clings to the term “greenhouse effect”, although his definition continues to “evolve”. Just recently, he stated that greenhouse gases act like a resistor. He presented a sketch of a simple electrical circuit with a voltage source (10 Volts) and a resistor (100 Ohms).

He then added a second 100 Ohm resistor behind the first one. He stated that that was analogous to adding greenhouse gases to the atmosphere. The second resistor (additional greenhouse gases) would “resist” energy flow (cause the planet to warm).

Well, there are so many things wrong with that analogy that I just had to laugh. But, I commented that the analogy might be closer to reality if the second resistor were added in “parallel” rather than in “series”. I mentioned that adding the resistor in parallel would increase current flow.

“Goddard” deleted my comment! :)

The fact is that adding a resistor in parallel does increase energy flow over the original circuit with only one resistor. This increased energy flow is analogous to increased heat transfer through the atmosphere to space, hence “cooling”. With only one 100 Ohm resistor in the circuit, the loop current would be 0.1 Amp. Adding a second 100 Ohm in parallel would increase the loop current to 0.2 Amp.

But, what is even funnier, “Goddard” really needs the resistor to be in parallel in his analogy, if he wants to claim “saturation”. In his mind, the reason global temperatures are not increasing, even though CO2 levels are increasing, is due to his “saturation” hypothesis. He claims that greenhouse gases “warm” only to a point, then their effect “saturates”, and the warming drops off. That is exactly the effect of adding increased resistance in parallel.